This competitive renewal application proposes to conduct a prospective study of pre-exposure biological and psychosocial characteristics, duty-related critical incident and routine work environment stressors, stressors and support outside of police service, and posttraumatic responses in police academy trainees who will be initially assessed during academy training, and followed every six months for the first two years of police service. The five primary aims of this proposed study are: (1) to determine prospectively if baseline psychosocial characteristics of police academy recruits explain posttraumatic stress and general functional disturbances following critical incident exposure during police service; (2) to determine prospectively if baseline biologic responses to laboratory stressors explain posttraumatic stress and general functional disturbances following critical incident exposure during police service; (3) to determine the role of cumulative critical incident exposure in explaining posttraumatic stress and general functional disturbances; (4) to determine the role of work environment, social support, and non-duty stressors in explaining posttraumatic stress and general functional disturbances; (5) to determine the role of peritraumatic responses in explaining posttraumatic stress and general functional disturbances. 480 academy trainees will be initially recruited (to insure a final N of 400), and followed for the first 24 months of police service. Baseline procedures include biological assessments (D.S.T., acoustic startle, physiological response to critical incident video), a clinical interview, and self-report questionnaires. At months 6 and 18, officers will complete self-report questionnaires; at 12 and 24 months participants will receive a Structured clinical interview and will complete a self-report packet. 20 percent of the sample will be selected based on symptom levels to be reassessed on acoustic startle and cortisol functioning.